Types of Chromosomes and

Human Genetic DisordersTypes of Chromosomes

KaryotypingSpecific disorders

Karyotyping

• Taking a photograph of chromosomes (usually from the blood) during mitosis and pairing them (homologous chromosomes paired) to see chromosome abnormalities.

Sex Chromosomes

• X: bigger chromosome than Y– 1200 + genes– Colorblindness, muscular dystrophy, hemophilia

• Y: much smaller– 140 genes

Autosomes

• 22 pairs (44 total)• Mutations of these chromosomes have a

greater affect on a person’s health

Disorders Caused by Individual Genes

• Sickle Cell Anemia: caused by a defective allele for a polypeptide in hemoglobin (protein which carries O2)– Makes hemoglobin stick together b/c

it’s less soluble and becomes sickle shaped

– Clogs capillaries to damage cells, tissue, or organs

Disorders Caused by Individual Genes

• Cystic Fibrosis: usually caused by a deletion of 3 bases (removal of phenylalanine from a protein) which causes the protein to be destroyed (recessive)– Leads to tissue malfunctions in

digestive system and causes thick, heavy mucus to clog lungs and breathing passageways

Disorders Caused by Individual Genes

• Huntington’s Disease: caused by a repeat of CAG (glutamine) more than 40 times– Symptoms include mental deterioration

and uncontrollable movements– The greater the # of repeats the earlier

the disease appears and it will be more severe

Disorders Caused by Individual Genes

• Advantages:– Those heterozygous for sickle cell anemia are

highly resistant to malaria and will not get either disease

– Proteins produced by CF block the entry of a bacteria that causes typhoid fever—those heterozygous for CF will have an advantage if they live in a city w/ poor sanitation and polluted water and won’t get either ailment

Chromosomal Disorders

• Nondisjunction: chromosomes don’t separate during meiosis get abnormal # of chromosomes– Trisomy: 2 copies of autosomes fail to separate so

you get 3 copies of a chromosome– Chromosome 21 = Down’s syndrome– XXX = sterile

• X chromosome nondisjunction can also cause XO = sterile(Turner’s Syndrome), or XXY = sterile (Klinefelter’s Syndrome)